MongoDB C# driver, query by an array element using regex -

i using mongodb c# driver version 2.2. collection contains "parent" objects. each parent object has array of children objects. each child has name value:

"parent": {     "children":[         { "name": "bob", "age": 10},         { "name": "alice", "age": 7},         { "name": "tobias", "age": 11}     ] } 

i need translate following code c# statements / linq syntax:

db.getcollection('parents').find({'parent.children': { $elemmatch: { 'name': { $regex: '.*ob.*', $options: 'im' } }}}) 

i have found there methods like

var builder = builders<bsondocument>.filter; builder.regex("parent.children.name", new bsonregularexpression(".*ob.*")); //does not work array 

and

builder.anyeq("parent.children.name", "ob"); //without regex 

but cannot understand how combine them. please advise.

update:

i using following now, please correct me if know reason why should not work correctly:

builder.anyeq("parent.children.name", new bsonregularexpression(".*ob.*")) 

i using following now:

builder.anyeq("parent.children.name", new bsonregularexpression(".*ob.*"))